A motor vehicle tank has an air venting system, with the assistance of which, pressure compensation is achieved between the interior of the tank and the surrounding ambient atmospheric air. The pressure equalization is created, for example, when, because of operation, fuel is taken from the tank or conversely, when upon refueling, the tank is being filled. The required addition and removal of air, respectively to and from the tank, associated with filling and emptying, results in a flow of air out of or into the tank interior. This air movement is taken care of, in most situations, by one or more devices installed or built into the tanks. The devices include, conventionally, a “roll-over” ball valve or a fuel level controlling valve. Added to these can be a fuel separator and an activated carbon filter to form an interface with the outer environment. These additions are mostly placed externally to the tank.
The individual components of the air vent system are connected among themselves by an air release line system, often in the form of flexible hoses. These lines, because of the complicated tank geometries found in today's motor vehicle tanks, are often supported by bottom hose supports. During a traveling period, that is to say, during a driving time of the vehicle, it is possible that liquid fuel can accumulate in the interconnected lines. This leads, then, to certain locations, wherein the lines form a downward curved, siphon-like shape, subject to gravitational flow of residual fuel. Due to fuel accumulating in the siphon, the necessary cross-section for air movement is reduced, whereby air flow through the passage deteriorates.
As an example of this flow restriction, during a refueling operation, such a high flow-resistant pressure is generated for the air trying to escape from the tank interior that it leads to a premature shutoff at the fuel delivery nozzle, which results in an incomplete filling of the motor vehicle tank.
An expulsion of the accumulated fuel from siphons in the air vent lines is possible only when the vehicle as a whole is somewhat sloped in a specific range of inclination.